The present invention relates to a recording apparatus and a recording method, and more particularly, to a thermal recording apparatus and a thermal recording method using the apparatus.
It has recently become more popular than before to record in colors the images of video camera, television, and computer graphics. This has aroused a sudden demand for colored hard copies. To meet this demand there have been developed color printers of various types.
Among various recording systems is the thermal transfer system which employs an ink sheet and a thermal recording head. The ink sheet has an ink layer formed thereon from an adequate binder resin and a transferable dye dispersed therein in high concentrations. In printing operation, the ink sheet is pressed under certain pressure against a piece of printing paper (or any other proper medium) coated with a dyeable resin which receives the transferred dye. Dye transfer takes place as the thermal recording head on the ink sheet generates heat in response to image signals. Thus the dye is transferred from the ink sheet to the printing paper in proportion to the amount of heat.
If the above-mentioned procedure is repeated for image signals separated into subtractive primaries (i.e., yellow, magenta, and cyan), it is possible to produce a color image having a continuous gradation. The thermal transfer system is attracting attention because it provides high-quality images comparable to those of silver halide color photography, it simply needs a small-sized, easy-to-maintain machine, and it operates on the real-time basis.
FIG. 1 is a schematic front view showing the important parts of a printer of the thermal transfer system.
There are shown a thermal recording head 61 (referred to as thermal head hereinafter) and a platen roller 63, which face each other. Between them are interposed an ink sheet 62 and a sheet of recording paper (transfer medium) 70. The ink sheet 62 is composed of a base film 62b and an ink layer 62a formed thereon. The recording paper 70 is composed of paper 70b and a dyeable resin layer 70a formed thereon. They pass over the thermal head 61 under pressure exerted by the rotating platen roller 63.
Upon selective heating by the thermal head 61, the ink (transferable dye) in the ink layer 62a is transferred to the dyeable resin layer 70a of the transfer medium 70. In this way thermal transfer printing in dot pattern is accomplished. Thermal transfer printing of this type is usually based on the line system which employs a long thermal head which is fixed at a right angle to the direction in which the recording paper runs.
Unfortunately, the line system has the following disadvantages.
(1) The ink sheet to supply ink is thrown away once it has been used. After printing, it becomes wastes, posing a problem with material saving and environment protection.
(2) In order to reduce the amount of ink sheet thrown away, it has been proposed a means to provide full-color images by using an ink sheet repeatedly. However, this system has a disadvantage that the second and subsequent printing is poor in quality because of "back transfer". In other words, when a first transfer dye A is transferred to a transfer medium and a second transfer dye B is transferred to the same transfer medium, the transferred dye A is transferred back from the transfer medium to the layer of the transfer dye B on the ink sheet.
(3) The ink sheet is bulky, and this limits the size reduction and weight reduction of the printer.
(4) Actually, the so-called thermal transfer system utilizes the thermal transfer of a dye. For a dye to diffuse into the image receiving layer of the transfer medium, it is necessary to sufficiently heat the image receiving layer, too. This lowers the heating efficiency.
(5) For efficient transfer, it is necessary to press the ink sheet against the transfer medium under high pressure. Any printer to meet this requirement has to be strong. This again limits the size reduction and weight reduction of the printer.
Since the thermal transfer system has many disadvantages as mentioned above, it is desirable to establish a technology to reduce the amount of wastes and transfer energy and to produce a small light printer, without sacrificing the above-mentioned advantages.
Other thermal transfer recording systems proposed so far are given below.
U.S. Pat. Nos. 4,772,582 and 4,876,235 disclose a method for transfer printing by the sublimation of a disperse dye which takes place upon irradiation with a diode laser. The dye is supplied from an ink sheet which is spaced away from printing paper by plastic microspheres. However, these patents merely describe a throwaway ink sheet coated with a binder resin in which the dye is dispersed.
U.S. Pat. No. 5,017,547 also discloses a method for transfer printing by the sublimation of a disperse dye which takes place when an infrared absorbing dyestuff added to the dye layer is heated by irradiation with a diode laser. The dye is supplied from an ink sheet which is spaced away from printing paper by microspheres. This patent merely describes a throwaway ink sheet coated with a binder resin in which the dye is dispersed.
They mention spacing with microspheres but they do not mention spacing with metal film or plastic film, nor do they mention anything about efficient light-heat conversion.
U.S. Pat. No. 4,541,830 discloses a method for ordinary thermal transfer printing with an ink sheet spaced away from printing paper by microspheres. This patent merely describes a throwaway ink sheet coated with a binder resin in which the dye is dispersed.
The prior art technologies mentioned above have not yet eliminated the above-mentioned disadvantages.